A new large-scale integrated metallization-failure mechanism

Abstract

A new integrated-circuit metallization-failure mechanism is reported. The aluminum metallization sometimes disintegrates during ultrasonic agitation despite the fact that the aluminium–silicon oxide–water system is thermodynamically stable under conditions normally encountered by integrated circuits. The disintegration reduces conductor cross section and increases the probability of failure by electromigration. Faulty batches of metallization from six manufacturers have been found; one batch of devices, which failed abnormally early through electromigration, had the faulty metallization.Scanning–electron–microscope examination revealed that foreign material or voids were sometimes visible between the aluminum grains but there was often no visible indication of the problem areas. Scanning Auger microprobe examination revealed nitrogen and oxygen in the aluminum of faulty batches, and carbon was also present in the areas that lifted. Aluminum, which was unaffected by ultrasonic agitation, had no additional elements.Experiments in controlling the evaporation environment to increase the probability of incorporating oxygen, nitrogen, and carbon into the aluminum layer were unsuccessful.Ultrasonic agitation provides an economic possibility for screening devices with unstable metallization. It can be introduced during wafer manufacture or as a sampling screen on completed devices for high reliability applications.